A ring binder mechanism retains loose-leaf pages, such as hole-punched pages, in a file or notebook. It has ring members for retaining the pages. The ring members may be selectively opened to add or remove pages or closed to retain pages while allowing the pages to be moved along the ring members. The ring members mount on two adjacent hinge plates that join together about a pivot axis.
A housing—typically metal and elongated—loosely supports the hinge plates within the housing and holds the hinge plates together so they may pivot relative to the housing. The housing has a generally arch-shaped cross-section, with bent-under rims that hold the hinge plates within the housing. The hinge plates are disposed within and extend across the open bottom part of the arch spaced from the top wall of the arch and the ring members extend through notches or openings in the housing.
The undeformed housing is slightly narrower than the joined hinge plates when the hinge plates are in a coplanar position (180°). So as the hinge plates pivot through this position, they deform the resilient housing laterally outwardly and cause a spring force in the housing that urges the hinge plates to pivot away from the coplanar position, either opening or closing the ring members. Thus, when the ring members are closed the spring force resists hinge plate movement and clamps the ring members together. Similarly, when the ring members are open, the spring force holds them apart. An operator may typically overcome this force by manually pulling the ring members apart or pushing them together. Levers may also be provided on one or both ends of the housing for moving the ring members between the open and closed positions.
Conventionally, the housing is mounted on the file or notebook with the open bottom part of the housing facing the file or notebook. Thus, the hinge plates are covered by the top wall of the housing. This configuration presents a generally solid metal surface as the exposed surface of the housing.
This exposed surface often has a nickel-containing plating, to which some people may be sensitive. Additionally, it is difficult and/or more costly to print on a metal surface—particularly where the metal surface is nickel-plated—in a manner that the printing is retained on the surface. Nickel plating can also present some environmental and work hazard issues.